Adds a section on notifications used by OP-TEE, synchronous and asynchronous. Reviewed-by: Sumit Garg <sumit.garg@linaro.org> Acked-by: Marc Zyngier <maz@kernel.org> Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org> Change-Id: I063b534da4cdd82966d039ab1a1ada1b5658534b Reviewed-on: https://gerrit.st.com/c/mpu/oe/st/linux-stm32/+/238036 Tested-by: Alexandre TORGUE <alexandre.torgue@foss.st.com> Reviewed-by: CITOOLS <MDG-smet-aci-reviews@list.st.com> Reviewed-by: CIBUILD <MDG-smet-aci-builds@list.st.com> Reviewed-by: Alexandre TORGUE <alexandre.torgue@foss.st.com>